United States presidential election, 1800

The election of 1800 was the first election that seriously challenged an incumbent for the Presidency. John Adams was attacked constantly by the supporters of Thomas Jefferson. The strain probably broke the friendship between the two candidates, although they mended it in the following years. While Adams performed reasonably well, he lost out to Jefferson.

Despite the problems encountered with the electoral system in the previous election, no change was made to it and so the inevitable happened: Jefferson tied on votes with his running mate, Aaron Burr, which led to a tie and vote in the House of Representatives. Largely out of spite, the Federalist-controlled House tried to reverse Jefferson's ticket and elect Burr as President, but lacked enough of a majority to force Burr's election. Eventually, Alexander Hamilton decided that Jefferson was the lesser of two evils and persuaded enough Federalists to switch their support to Jefferson, finally resulting in his election.

The incident had massive repercussions, forcing the electoral system to be changed, souring the relationship between Jefferson and his Vice President, who had refused to back down and sought the Presidency himself, and leaving a lingering mutual hatred between Burr and Hamilton, which eventually lead to the duel that claimed Hamilton's life and resulted in Burr's political ruination.[1][2]